Anti-Drug Antibody (ADA)
An antibody produced by a patient's immune system against a therapeutic peptide drug. ADAs may be neutralising (blocking the drug's activity) or non-neutralising (binding without blocking). ADA formation is monitored throughout peptide drug development and can affect treatment efficacy and safety.
Technical Context
ADA characterisation includes: binding antibody titre (quantifying ADA level), isotype determination (IgG, IgM, IgE — IgE suggests allergic potential), epitope mapping (identifying which part of the drug the antibody recognises), neutralising capacity (does the ADA block the drug's receptor binding?), and cross-reactivity (does the ADA also bind the endogenous counterpart — critical safety concern). Clinical consequences of ADA: reduced drug exposure (enhanced clearance through immune complex formation), reduced efficacy (neutralising antibodies blocking activity), altered PK (forming drug-antibody complexes that change distribution and elimination), hypersensitivity reactions (IgE-mediated or immune complex-mediated), and rarely, cross-reactive neutralisation of endogenous protein (e.g. ADA against exogenous EPO cross-reacting with endogenous EPO, causing pure red cell aplasia). Most ADA formation is transient and clinically inconsequential.